An MRI apparatus provides a tomographic image indicating physical and chemical characteristics using a magnetic nuclear resonance phenomenon generated by irradiating high frequency pulses to an inspection object placed in a uniform static magnetic field and is particularly used for medical applications. The MRI apparatus mainly includes a static magnetic field coil device for generating a uniform static magnetic field in an imaging region into which the inspection object is inserted, a gradient magnetic field coil device for generating a gradient magnetic filed of which magnetic intensity spatially varies to have a gradient to apply positional information to the imaging region, an RF coil for irradiating high frequency pluses to the inspection object, a receiving coil for receiving a magnetic resonance signal from the inspection object, and a computer system for processing the received magnetic resonance signal to display the tomographic image.
To improve the MRI apparatus, increase in a magnetic field intensity of the gradient magnetic field and a high speed pulse driving for the gradient magnetic field are considered. These, contributing to shortening an imaging time and improvement in image quality of the tomographic image, are frequently used in a high speed imaging method. This is because an improvement in performance of a driving power supply for the gradient magnetic field coil device allows a high speed switching and a large quantity of current to flow therethrough.
However, the large quantity of pulse current, i.e., a large current having steep variations in waveform, flowing through the device causes eddy current in the gradient magnetic field device. A heat generated at the gradient magnetic field device due to the eddy current increases temperatures thereof and in the vicinity of the gradient magnetic field device. The eddy current, generating an unnecessary magnetic field in the imaging region, decreases an accuracy in gradient of the gradient magnetic field.
JP 10-216102 discloses, in FIG. 6, a method of suppressing generation of the eddy current by using a plurality of thin lines as lead lines connected to the gradient magnetic field device.